VLAN tagging during Linux installation in VMWare ESX : Linux guest OS in VMWare unreachable/unpingable

I would like to just zoom into my specific problem here :

The HP Proliant 480C comes with a Layer3 switch (Gbe2c model) built in :

a)we have succeeded in building a Windows guest client  inside this VMWare
   server earlier.  The Windows client has an  IP addr 10.51.x.y  &  it uses the
   very same switch & is able to get connected to other LANs.  So from this
   Windows client, I'm able to ping to other servers on other subnets & vice-
   versa

b)however, after building this Linux ESX inside the same VMWare, it's able to
   to boot up fine, just that it's unable to even reach the built-in Layer 3 switch:
   From this Layer3 switch, I'm able to ping to the Windows guest client
   10.51.x.y  but  from this built-in Layer3 switch, I'm unable to ping to the
   Linux client (172.17.y.z) (with vswif0 interface up & running)

c) I then tried to configure an IP addr for eth2 (172.17.y.t) in this Linux client
   but it did not help make this Linux client reachable from anywhere

Is there a firewall within Linux which could have prevented these connectivity
& if so how do we disable it?

During installation of Linux, there's a screen for "Tagging" where we can key
in a VLAN id - what is this for?

Do we need to create a VLAN on the switch for the Windows OS & another
separate VLAN for the Linux OS?